The present invention is a new prototype of a continuously variable transmission system. It will be used as the gear box in automobiles, motorcycles or any other self-propelled vehicle requiring a variable transmission ratio between the power plant and the live axle.
This system offers noteworthy improvements in the theoretical concept and practical undertaking of existing transmission systems based on the same mechanical principles. These improvements consist in a simplified design and a broader generalization of the kinematics design.
This invention has practical applications in all systems requiring continuous regulation of rotational speed and torque supplied by a power plant.
This invention pertains to section F. Mechanics, in accordance to C.I.P.
Internal combustion engines are the most widely used power plant for automobiles and in self propelled vehicles in general. Their main advantage is the high specific power (power per unit weight) which they are capable of supplying, as well as their high autonomy. They do, however, have one disadvantage: the limited range of speeds at which they are able to produce high enough power. In general, they only produce sufficient power for automotive use between approximately 1000 and 6000 rpm. Moreover, the power output differs from one regime to another, the maximum power being five or six times that found at idle speeds.
If the transmission ratio between the engine and the wheels of the vehicle were fixed, the whole range of speeds required by the vehicle would not be encompassed. In fact, a relation which provides an adequate minimal speed (e.g. 10 km/hour) yields an inappropriate maximum speed (60 km/hour). Analogously, a fixed relation which provides a commercially acceptable maximum speed (e.g. 210 km/hour) would yield an unacceptable minimum speed (35 km/hour). This was the main reason leading to the incorporation of a variable ratio transmission system, generally known as a gear box.
Conventional gear boxes allow for selection among a discrete range of transmission ratios, usually between 4 and 6 for passenger vehicles, a few more for commercial and 4-wheel drive vehicles and buses, and double and triple for agricultural and construction vehicles. Better use is made of the engine with these boxes. Any value of vehicle speed can be reached while maintaining relatively high power output, within an appropriate range of speeds. However, these transmissions are not ideal, since they are only capable of providing maximum engine power for certain values of vehicle speed. Continuously variable transmission appeared in an attempt to evade this inconvenience; this technical solution being capable of providing any ratio between vehicle speed and engine angular speed. In this way the engine could be kept rotating in the most convenient regime no matter what speed the vehicle were traveling at. In principle, this regime could be the one of maximum power, but the maximum torque regime, and the minimal specific fuel consumption regime, are also of interest.
The present development of transmission systems can be classified as follows:
Fixed ratios. These use sets of spur gears which mesh giving way to a transmission ratio which depends on the diameters of the gears involved. The ratios vary depending upon the wheels which mesh and intervene in the transmission chain. This system requires clutches in order to carry out the ratio selection. These selections can be made manually or automatically, the second case requiring a hydraulic system, called a hydraulic torque converter, as well as planetary gear sets. Electromechanical clutch systems have also been used for this purpose.
Continually variable ratio. In this scope there are a wide variety of ideas and practical developments. The different types over time can be classified as:
Hydraulic systems. They use variable displacement pumps.
Systems based on belt transmissions. From a practical point of view, the Transmatic Van Doorne system is one of the most widely used. It is based on a belt transmission between pulleys which can vary their effective diameter, thus changing the transmission ratio. Some of the drawbacks of this type of system lie in its excessive volume and low capacity of power transmission. The latter is due to the system being based on friction. Other configurations worth mention are those developed from the work of Fouillarion, the Kumm mechanism, the PIV -Reimers, Variomatic, etc.
Systems based on wheels in contact. Known as traction drives. They basically consist of two wheels in contact with their perpendicular axis which vary the transmission ratio as one wheel moves away from the axis of the other. This system is also based on friction and it requires pure rolling contact. The most noteworthy mechanisms are NTD (Nutating Traction Drive) by Vadetec, Vadetec NT-XA2, Hayes CVT toroidal, Perbury/BTG toroidal CVT, the developments by Excelermatic, Forster, Epicyclic by Jaguar and Torotrak, among others.
Oscillating systems. These are completely mechanical transmissions which transform a rotating movement into an oscillating one. This is latter rectified in the kinematic chain by converting it back to a rotational motion. They are known as ratcheting drives. They have a few advantages: they do not involve friction elements, they do not need clutches, the transmission ratio can be varied with a simple linear actuator without transmission interruptions and they are smaller, lighter and cheaper to manufacture than an automatic gear box. Some of the first inventions of this type of mechanism were the R. V. R, Dietrich and LCB systems. One of the most recent practical realizations is the system developed by Epilogics Inc. Called infinitely variable transmission (IVT), it is the object of the P. Pires patent.
The advantages of the system which is the object of this patent can be synthesized as follows:
Completely mechanical transmission and, therefore, high mechanical efficiency.
Absence of friction elements which reduce the efficiency of torque transmission.
The transmission ratio continuously varies linearly from 0 to 1. This ratio may be varied with an extra multiplying or dividing system.
There is no need to interrupt the power flow (via a clutch) to vary the transmission ratio from a null value to a non-null value or from a non-null value to zero.
The above characteristics make the system especially interesting from an industrial and commercial point of view. It has an immediate application in the automobile industry, as well is in industrial applications requiring speed and torque variations
The main differences between this system and the system which is technologically closest to it, the IVT mechanism by Epilogics U.S. Pat. No. 4,983,151 A), are:
There are no elbow members to transform the rotating input into oscillating motion.
There is one sole epicyclical mechanism and, therefore, there is no direct transmission through a secondary axis from the power plant to be added to the output of the rectifying mechanism.
The aim of this patent is the design of a torque-velocity converter which improves upon current oscillating systems which conform the state of the art up to the present. The system, an outline of which appears in FIG. 1, allows for the transformation of the input torque (Me) at angular input speed xcfx89e into another output torque (D) at angular speed xcfx89s. This transmits the power entering through the input axle to the output axle, this transmission of power being affected by the mechanical efficiency of the system.
The system is made up of three sub-systems which will be described below:
Torque-Speed Variation Sub-system. Its aim is to vary the relative position of the Transformation and Division Sub-system with respect to the Compounding Sub-system.
Transformation and Division Sub-system. This mechanism transforms and divides the power entering through the primary axle, characterized by torque Me and angular speed xcfx89e, at power transmitted to various secondary axles, characterized by oscillating torques and angular speeds.
Compounding Sub-system. This mechanism compounds the power transmitted by the secondary axles, using an epicyclic gear train, into an output power characterized by torque Ms and angular speed xcfx89s.